1. Field of the Invention
The embodiments of the invention generally relate to electrodeposition of alloys and, more particularly, to a multi-anode system and method for electrodeposition of alloys.
2. Description of the Related Art
Generally, electrodeposition is a process in which a workpiece to be plated is placed in a plating container with a plating solution (i.e., plating bath). An electrical circuit is created when a negative terminal of a power supply is connected to the workpiece so as to form a cathode and a positive terminal of the power supply is connected to another metal in container so as to form an anode. The plating material is typically a stabilized metal specie (e.g., a metal ion) in the solution. During the plating process this metal specie is replenished with a soluble metal that forms the anode and/or can be added directly to the solution (e.g., as a metal salt). When an electrical current is passed through the circuit, metal ions in the solution take up electrons at the workpiece and a layer of metal is formed on the workpiece.
Several methods have been developed for depositing an alloy of two or more different metals (e.g., nickel and cobalt) on a workpiece, based on the above-described electrodeposition process. In one method, a single anode is used that comprises one of the plating metals and any additional plating metals are contained in the plating bath. However, to control the composition and residual stress of the deposited alloy, the plating bath requires frequent chemical additions and eventual dumping. That is, the level of the metal salts in the plating bath buildup over time and in order to keep the metal salt concentrations within normal plating levels, the plating bath must be periodically removed and replaced. If this is not done, the residual stress of the deposit will increase. In another method, an anode that comprises an alloy with the predetermined metal ratio is used. The use of the alloy anode, resolves the need for chemical additions and periodic dumping of the plating bath. However, it is basically impossible to modify the alloy metal ratio once the electrodeposition process has started because the ratio of the deposited alloy is for the most part determined by the ratio of the metals in the anode. In yet another method, multiple rectangular-shaped anodes are placed against one side of the container and spaced apart, as illustrated in FIG. 1. These rectangular-shaped anodes comprise different type metals and are connected to separate voltage sources. This method allows the ratio of metals in the alloy plate to be selectively controlled by applying different current values to anodes with different type metals. However, varying currents in this manner produces a non-uniform voltage profile in the plating bath that typically results in both a non-uniform alloy composition and a non-uniform thickness as compared to the above-described methods. Therefore, there is a need in the art for an electroplating system and an associated electroplating method for depositing metal alloys that does not require periodic plating bath removal or an alloy anode and that does allow for both deposition thickness control and dynamic metal ratio control.